Photometer.



A. P. mmf.

P HoToMETEn. APPLICATION FILED SEP'T- 3. 19| I- Patented Dec. 17, 1918.

New

' UNITED PATENT oEEIoE. I AELIEGTQN P. LITTLE, 'or w-AsHINGToN, nIsTnIoT oF COLUMBIA.

Washington, D. C., in thel Districtv ofColumbia, 'have invented a new and useful Photometer, Vof which -thefollowing is a specification..

M; invention relates to a photometer emple ing .a surface 'endered luminous by a sel -lummousmateriah la's thecomparison screen; and has for its object a photometer capable of measuring b means of a comarisen surface, rendere luminous b a'selfuminous material, thefapparent brightness l' transparent disk which is 'nali section through the whichI sphere, h which support 1s fastened to a cross section of the apparatus on the line A+B of Fig. l. Fig. 4 is allongitudinal section .through anelbow attachment.

Similar characters of reference designate similar'parts throughout the several views.

The cylinder-shaped casing 1 is closed at one end and overthe open end of said casing is placed the cover 2. 3 is the enlarged end .of a rotatable shaft 4 which shaft hasone end threaded to receive nuts 5 and 6. 7, 7 are washers between which is the light-conf trol shutter or disk 8, said disk being firmly' securedto shaft 4 and rotatable therewith.

9 is acolor filter, 10 a removable semiused'to intercept a certain proportion o'f light before said light enters the Photometer. 11, i s a tube passes through the cover 2 and is y attached thereto.

firml held in position by the support 13, the instrument case 1 by means of the screws 14.- The interior-.of the spherez12 is partly or entirely coated with a self luminous material, for example `amixture of radium Spe'oication of Letters Patent. hunnen ileuuptenber 5,1917 serial No. 190,373.

vBe it known that I, ARLINGTON PfLrrrnE, a citi'zen ofthe United "Statfes, residing at vspect to the tube 2J..

`. shaft the pointer 2 6 A transmission "of this outer 12 is a hollow or a radium com-T1 vsuch as Gated on Patented Dec. 17, 1918.`

in the top of the sphere through which the interior of the sphere may be viewed, particularly that portion in the vicinity of 19 which constitutes the comparison screen of the photometens l16 is a reflecting surface on which falls the li ht which passes through the light controdisk 8.' 18 is the support for the reflector 16,4 said support belng -fastenedto 13 'byxneans of the screws The tube 21 passesthrough the case l and is'firmly attachedthereto The sight tube 20 is movable-longitudinally with re- .22is 'a lens secured to the inside of the Vtiibe 20. 2 3 is a disk or ring having an opening 24, said opening serving-to'limit the extent ofthe field seen through Ythe .sight tube.l *The disk 23 .is

heldin position bymean's of the bent wires 25,25. 26 is a' polnterwhi'ch vis, firmly secured to the. shaft 4 :and on .rotating the playal over a graduated scale 2 7 which is shown iny Fig. 2.` The handle 28 'permitsthe photometer to be held conveniently.- 31' 'i s a short tube removably attached to tube l11 Vand .as a translucent disk 32 fixed atits outer end. A33 is a lightshield tube, whose `function is to prevent stray light from impinging on the screen 32. The outer portion of the disk 8 passes behind the opening in the tube 11., The light portion or ring is less in the region 29 than it 1s at 30, and the 4light transmission factor changes in passing around this ring from one position to another, as is indicated 'by the relative spacing of the radial .lines on the disk 8 .as shown in Fig. 3.

Fig. 4|sho'ws an elbow 36 that may be slipped overftube 33, this elbow having a mirror 37 fastened therein and making an angle of 45 degrees with the axis of either arm of said elbow. The function of the mirror 37 is to chauve the direction of the light entering the elbow 36, which under certain conditions renders thephotometer 'more convenient to use.

he wire ring 35 seigves to hold the disk 10 in osition. `he surfaceemployed asthe comparison screen may be of any desired shape land contour, and the self-luminous 'material may be eld in ,position by Vany convenient means', a surface, inclosed in a transparent container. 'lhe advantage of elliflo'yi11g' a spherebr other 'inclosure is to obtain a relatively lhigh intensity of illumi- `nation and light nation on the comparison screen i9, because the light emitted by the sel-t luminous lining of the inclosure illuminates the screen 1921s does also the light reflected from the interior surfaces. I may use in my invention either a.. sphereshaped inclosure as shown,A or an inclosure of any other form, orthe inclosure may be omitted. The illumination on the comparison Screen may be produced, if desired, entirely ley lightv emanating from self-luminous surfaces in close proximity to seid screen or the screen may be coated more or lees with a self-luminous material.

Any known method may be .used'to con trol the intensity of the light falling on the screen i6. 2 .i

u The operation of the photometcr is illustrated by it is desired to iind the candle-power oa y certain type of lamp. The photom-eter would be held in such a position that directt light from the. lamp enters the tube 33 and illuminates the translucent disk 32, Thel disk becomes a, secondary source of illumithcrefrom passes through theveolor filter 9 and through the light con-l trol disk 8 and illuminates the screen 16.l 0n looking through the sight tube, which consists oi eyepiece 34 and tube 2O two illunni-l nated fields willy he seen, adjacent to each other, one being the screen 16 illuminated by the light from the .lamp Whose candle power is to he measured, and the other nein the comparison field 19. The knob 3`an the light control disk 8 which isattached thereto is then rotated until the two fields 16 and 19 are of equal brightness and the position of -the pointer 26 on the scale 27 is note'd. By referring to calibration data which gives the reduction factor for the type of lamp under test, the yiu'lt'ensity of illumination falling on the surface 52 may be de termined, and the candlepoiver of 'the lamp may be calculated in the usual Way;

-The lightdrom self luminous compounds is practically monoslironia'tic, hence 'if all colors are filtered out ci the light coming from the extern'al'source of light except that corresponding to the color of the light emit` (ed hy the Aself luminous material, an observer will he hotter able to judge equality oi." illumination between 'the comi'u'xrison lield and the externally illuminated field than if the fields observed were of differing colors, espcrially when the intensity of illumination is suliicient for the eye to perceive colors dist-inetly. ln lieu oi' the color -filterdescribed,v any known flicker attachment may he used.

The sight 'Luhe and tube ll may he provided with opaque caps or other suitable means for preventing an excessive amount l fields 1G and the following example: Suppose',

" screen adapted `sity lsure for said screen `throughwhich the screen, ran indicator `in coimection of light entering the photometer vvhen it is not in use.

rlhis instrument i-nay also be used an exposure meter in taking photographs, and for this purpose the scale 27 may be marked in such a way that the pointer will indicate the proper time exposure. In using-the instrmnent the tube is directed toward the rolijcct or objects to be photographed, the knul-led head 3 turned until` the photometer I 19 as viewed through the sight tube are of equal brightness and then note the indication oi' the pointer .E2G on the scale A27. w The object ofthe removable semi-transarent disk 10 is to absorb acertain part ot the light falling upon it and thus adapt the Aphoto'rneter to measure illumination of a 'higher intensity than could `be measured with the disklO removed.A

What I, claim aud'desire to secure by Letl. 'Ina pliotometer, the combination of a lto he illuminated by the light whose intensity is to.,heminisurcd` a ine-ans' of varyingr the intensity of thelight falling on said screen, an indicrtor, a` sight tube, a comparison screen' and an inclosure Vfor said screen the surface or suracesot said inclesure supporting,` a self luminous material.

2. In' a photometer, the combination olE a screen illuminated by the light whose intenis t0 be measured, means for varying the intensity of the light illun'iinating said screen, an indicator in connection with said mcans,a comparison screen, and an inelohaving an opening screen may be viewed and having its inner surface coated with a self luminous ymaterial adjacent, to the screen.

3. ln ayphotometer, the combination of a screen illuminatedhyjtlie light whose intellsity is to ne measured, means for varying the intensity of the light illuminating, said screen, an indicator in connection with said means, .and an inclosure having an opening in the line of vision when theilluminating screen is viewed, the inner surface oi' which inclosure iscoatel'with a seit' luminous material toimfm. a comparison screen,-

Llj'ln a photoincter, the combination of a screen' illuminated bythe Alight whose intensityis to he incasurci'l, means otvaryiug the intensity 'of ihrlfght 'falling upon said with said means. and a glotc yharing; anl opening;r adju'- e'ent to the illuminated screen, the inner surface o'which globe is coated with a self luminous material to form a comparison lll() 

